Front-side illuminated light sensors are well known in the art. The photosensitive region on the front side of the light sensor generates charges when exposed to light. Those charges are accumulated during an integration phase within the photosensitive region and transferred to a memory area. During a next integration phase, the previously transferred charges are read out from the memory area using a read circuit.
It is important for the light sensor to include some optical shielding. For example, optical shielding may be provided between adjacent light sensors in an imaging array in order to ensure that the light directed toward one photosensitive region does not impinge on an adjacent photosensitive region. Additionally, optical shielding may be provided within the light sensor over the memory area in order to ensure that light directed toward the photosensitive region does not additionally generate charges in the memory area.
A premetallization dielectric (PMD) layer is typically provided at the front side of the light sensor. Metal substrate contacts pass through the PMD layer to electrically connect the integrated circuitry in and on the substrate to the metal lines supported within overlying metallization layers. There is a need in the art to support both metal shield trenches and metal substrate contacts within the PMD layer.